Speech sound detection apparatuses are well-known in the art that are used to determine whether or not input sound is speech sound (vocal sound uttered by a user). One example of this type of speech sound detection apparatuses disclosed in Patent Document 1 listed below has a plurality of microphones.
Such a speech sound detection apparatus receives an audio signal input through every one of the microphones. The speech sound detection apparatus computes input power that indicates a magnitude of sound represented by the audio signal (i.e., input power of the audio signal). The speech sound detection apparatus determines, based on the computed input power, whether or not the sound represented by the audio signal input through the microphone is speech sound.
As is prone to be with this type of the speech sound detection apparatuses, when input through more than one microphones, the same sound is represented in different levels of input power that indicate magnitudes of the sound represented as audio signals collected through the microphones (i.e., input power of the audio signals) because of dissimilarities inherent to the microphones, different degrees of deterioration over time, divergent types of signal transmission system (e.g., wiring), and the like.
In such a case, it is impossible to determine, based on some fixed criteria, whether or not the sound represented by the audio signals input through the microphones is speech sound. This means that accurate determination is impossible for each of the sounds acquired by such more than one microphones. To address this, it is deemed suitable to apply a signal correction device for correcting the input power of the audio signals received through the microphones.
An example of this type of signal correction devices is the one disclosed in Patent Document 2 listed below which receives audio signals input through one of microphones and computes a magnitude of input power of the received audio signals at every frequency range. Then, the signal correction device further computes a rate of the reference power used as a criterion (e.g., an average of all the magnitudes of the input power of the audio signals input through every one of the microphones) to the computed input power at every frequency range so as to determine a correction coefficient depending upon the computed rate.
Eventually, the signal correction device corrects the input power of the received audio signals based upon the correction coefficient thus determined. In this way, the input power of the received audio signals can be approximated to the reference power at every frequency range. Thus, applying the signal correction device to the speech sound detection apparatus enables accurate determination on whether or not the input sound through the microphones is speech sound.    Patent Document 1    Official Gazette of Preliminary Publication of Unexamined Japanese Patent Application No. 2008-158035    Patent Document 2    Official Gazette of Preliminary Publication of Unexamined Japanese Patent Application No. 2007-68125